1. Field of the Invention
The present invention relates to an organic light emitting device (organic electroluminescence device) for emitting light through energization of an organic layer including a light emitting layer formed between electrodes, and more particularly, to a multicolor organic light emitting apparatus having a plurality of organic light emitting devices formed on a substrate, for exhibiting two or more luminescent colors.
2. Description of the Related Art
In general, as a self-emitting device used for a display, a light source, or the like, an EL (electroluminescence) or an LED (light emitting diode) is known. Particularly, an organic light emitting device in which an organic compound material is used as a luminous body has been focused because it is possible to obtain luminance of several hundreds to 1,000 Cd/m2 or more at a low voltage of about 10 V or less (when the device is DC driven).
Further, by appropriately selecting an organic compound material having emission spectrums corresponding to red (R), green (G), and blue (B), it is possible to produce an organic light emitting device for exhibiting three primary colors, and it is also possible to produce a full color display having a plurality of organic light emitting devices formed on a substrate with relative ease. From this point of view, at present, studies and development of the organic light emitting device are vigorously conducted.
However, a thickness of an organic layer of the organic light emitting device is the same as or less than that of an emission wavelength. Therefore, in order to obtain an organic light emitting device having a desirable luminous efficiency, it is necessary for the organic light emitting device to be designed in view of an influence of optical interference.
Accordingly, the following techniques are disclosed as a technique of optimally designing the organic light emitting device from an optical point of view.
Japanese Patent Application Laid-Open No. 2000-323277 discloses an organic electroluminescence multicolor display having a plurality of organic electroluminescence devices which is formed on a transparent substrate and in which a light emitting layer is made of a different material from the other, and which exhibits various luminescent colors. In addition, functional layers having the same function as that of the organic compound material layer other than the light emitting layer have thicknesses different from each other corresponding to each luminescent color. In other words, by varying each thickness of a hole transporting layer, an electron transporting layer, and the like for each luminescent color, optically optimum conditions for each luminescent color are satisfied.
Thus, Japanese Patent Application Laid-Open No. 2000-323277 describes that it is possible to provide an organic EL multicolor display having a desirable external light extraction efficiency with a simple method as compared with a conventional method of satisfying the optically optimum conditions by partially changing a thickness of an ITO anode.
Further, Japanese Patent Application Laid-Open No. 2000-323277 describes that a distribution of an emission intensity in the light emitting layer of the organic EL device formed of the organic compound material layer corresponds to an index function distribution with respect to a thickness, in which the emission intensity is strong on an interface on the hole transporting layer side, and the emission intensity decreases toward the electron transporting layer side. In addition, it is described that the interface on the hole transporting layer side is known as a light emitting interface having an emission intensity peak (see paragraph [0040]).
Further, Japanese Patent Application Laid-Open No. 2004-127795 discloses a display apparatus including a light emitting layer between a first electrode and a second electrode, and an organic light emitting device having a resonator structure in which light emitted from the light emitting layer is resonated between a first end portion and a second end portion. In addition, for respective organic light emitting devices for red emission, green emission, and blue emission, a maximum emission position of the light emitting layer and an optical distance between electrodes that sandwich the light emitting layer are defined. In this case, the thicknesses of the hole transporting layer, the light emitting layer, and the electron transporting layer of the organic light emitting devices for each color are different from each other, and all the thicknesses of the organic layers are adjusted (see paragraph [0045] to [0050])
Thus, Japanese Patent Application Laid-Open No. 2004-127795 describes that it is possible to obtain a relationship in which reflected light and generated light are mutually enhanced between the first end portion and the second end portion, which improves an extraction efficiency of light generated in the light emitting layer.
Further, Japanese Patent Application Laid-Open No. 2004-127795 describes that the organic light emitting device for red emission emits light on an interference on a side of the first electrode which is a anode, but the maximum emission position is on an interface on a side of the second electrode because the light emission on a side of the second electrode which is a cathode is larger than that on the first electrode side. The organic light emitting devices for green emission and blue emission emits little light on the side of the second electrode which is a cathode, so the maximum emission position is on the interface on the side of the first electrode which is a anode (see paragraph [0031]).
However, in both the organic EL multicolor display described in Japanese Patent Application Laid-Open No. 2000-323277 and the display apparatus described in Japanese Patent Application Laid-Open No. 2004-127795, the thicknesses of the hole transporting layer and the electron transporting layer are varied, which are unnecessary to be varied for each luminescent color if the optical interference between the light emitting layer and the reflecting electrode is not utilized. As a result, there arises a problem in that the number of manufacturing processes is drastically increased. In addition, it is necessary to severely control an alignment accuracy of a mask necessary for varying the thickness for each luminescent color, and an impurity or the like generated when the mask is exchanged, which leads to a reduction of a yield. Because of those problems, it is extremely difficult to vary each thickness of the layers having the same functions for each luminescent color in an actual manufacturing process. As a result, there is a demand for improving the external light extraction efficiency for each luminescent color by varying each thickness of the layers for each luminescent color not with the structure described in Japanese Patent Application Laid-Open No. 2000-323277 or Japanese Patent Application Laid-Open No. 2004-127795 but with a simpler structure.